1. Field of the Invention
This invention relates to machines used to form curbing and the like. More particularly, this invention relates to lightweight portable apparatus for extruding, shaping and laying continuous concrete curbing and similar elongate structures from mortar.
2. Information Disclosure Statement
Numerous patents exist which describe machines for laying street curbing. These machines are very large and require several, and sometimes up to eight or more persons to operate satisfactorily. One such machine is described in U.S. Pat. No. 3,600,773, to Davis. Concrete forms a curb in a mold as the machine is pulled by a winch-cable system. The machine is not adaptable to lay curbing in other than a straight line. Furthermore, the concrete is not extruded by an applied force, but is merely laid in the mold.
Other large machines for forming curbs or curb-like structures, each utilizing a ram for extruding the concrete, are described in U.S. Pat. Nos. 3,507,015 to Heatlie, 3,292,511 to Cheney, 3,530,552 to Calder, 3,363,524 to Catenacci, and 3,605,580 to Miller. The sinusoidal velocity profile of the ram results in an extrusion velocity cyclically varying between a maximum value and zero, or even between a maximum value and a smaller negative value. The velocity generally is zero or negative for one-half of the cycle. Thus, the actual mean velocity is always much lower than the desired maximum. Although the ram period may be shortened to smooth out the concrete movement from the extrusion mold, up to one-half of the motive energy is wasted by reverse movement of the ram through the concrete in each cycle. Furthermore, in order to prevent the ram from reversing the movement of concrete on the return stroke, thus destroying the curb integrity, these machines are designed to provide a large amount of slip. This also wastes considerable energy.
Some existing machines are driven by a single speed motor which extrudes a nearly constant mass of concrete per unit time. Since larger curbing requires more material per running foot, laying speed will be inversely proportional to the cross-sectional area of the curbing. Motors limited to driving the machine at a single speed cannot provide the range of speeds required for different sizes and shapes of curbs.
Curb laying apparatus which use an auger to compress the concrete or asphalt paving material are much more efficient than ram-operated machines, because the concrete or mortar is moved continuously forward at a velocity dependent upon the easily controlled auger speed (revolutions per minute). Thus, the machine may be operated at the optimum velocity for forming the particular curb. U.S. Pat. Nos. 3,053,156 and 3,261,272 of Jennings show a curb-laying apparatus using a belt-driven auger to pressurize the concrete. Front wheels and rear wheels are located near the forward and rearward extremes of the long machine, and when turns are made in a short radius, the discharge end of the mold becomes misaligned with the already-laid curbing. Canfield U.S. Pat. No. 2,707,422 shows a similar machine having somewhat different construction.
Another machine is described in U.S. Pat. No. 3,915,584 to Cobo, Jr. et al. This apparatus uses two coaxially aligned augers which allow curbing to be laid in either direction from the same side of the machine. In order to achieve a reversal of direction, the hopper must be removed from one auger and attached to the other auger, the front and rear wheels are interchanged, the mold is removed from one auger end, a mold of reverse configuration is attached to the other auger, and a cover means is secured over the open unused auger inlet as a safety measure.
Smith U.S. Pat. No. 3,137,220 describes a curb laying machine utilizing multiple augers to balance the extrusion forces within the mold.
All of the aforedescribed apparatus are designed for laying street curbing. The laying of decorative curbing differs considerably, since the use of datum and guide lines or forms is not practical. Decorative curbing is much smaller in cross-section than street curbing, and typically is laid serpentine fashion to enclose plantings, flower beds, trees, and the like. Often, it is desired to abut the curbing ends against structural foundations, walls, or other objects. Street curbing machines are too large and bulky, and have a wheel base too large to negotiate the short radius curves and limited operating space where decorative curbing is typically laid. They are not easily portable.
Simple hand-operated ram machines are shown in U.S. Pat. Nos. 3,733,140 and 3,733,141 of James, III. These machines are useful only for limited curb laying, because they are slow, cumbersome, and labor intensive.
A small curb extrusion device is shown in U.S. Pat. No. 4,566,823 of May. Concrete or other moldable material is extruded through a mold by the action of a motor-driven ram. The machine is limited by its ram operation to a cyclical speed whose average is considerably less than the desirable maximum speed for laying curb, and much energy of the motor is wasted. Changing molds is time consuming because disassembly of various parts is required. In addition, the cyclic ram movement tends to produce curbing with uneven cross-sectional area.
A problem particularly with any small ram-operated curbing machine is that unless it has a short stroke and is operated at high RPM, it may tend to produce curbing with alternating high compression and low compression sections.
Furthermore, the reciprocating ram operation makes it difficult to produce the curbing along the desired path, even when guide strings are used; the machine may tend to weave away from the path. Often, the curbing is later pushed into the desired path with a board. This must be done before the curbing hardens, and in any case may weaken the curbing. In large, street curbing machines, the use of at least four wheels provides four-point support to prevent the machine from wandering from the guide line.